Organophotoreceptor with a charge transport material having two epoxidated-hydrazone groups

ABSTRACT

Improved organophotoreceptor comprises an electrically conductive substrate and a photoconductive element on the electrically conductive substrate, the photoconductive element comprising: 
 
(a) a charge transport material having the formula  
                 
         where Y 1  and Y 2  are, each independently, an arylamine group;    R 1  and R 2  comprise, each independently, H, an alkyl group, an alkenyl group, a heterocyclic group, or an aromatic group;    X 1  and X 2 , each independently, are bridging groups;    E 1  and E 2  are, each independently, an epoxy group; and Z is a linking group comprising an alkyl group, an alkenyl group, a heterocyclic group, or an aromatic group; and (b) a charge generating compound. The charge transport materials can be crosslinked to a polymeric bind, either directly or through a crosslinking agent. Corresponding electrophotographic apparatuses and imaging methods are described.

FIELD OF THE INVENTION

This invention relates to organophotoreceptors suitable for use inelectrophotography and, more specifically, to organophotoreceptorshaving a charge transport material comprising at least two epoxy groups,each bonded directly or indirectly through a bridging group to anitrogen atom of a hydrazone group. Each epoxy group may or may not becovalently bonded with a polymeric binder, directly or through acrosslinking compound.

BACKGROUND OF THE INVENTION

In electrophotography, an organophotoreceptor in the form of a plate,disk, sheet, belt, drum or the like having an electrically insulatingphotoconductive element on an electrically conductive substrate isimaged by first uniformly electrostatically charging the surface of thephotoconductive layer, and then exposing the charged surface to apattern of light. The light exposure selectively dissipates the chargein the illuminated areas where light strikes the surface, therebyforming a pattern of charged and uncharged areas, referred to as alatent image. A liquid or dry toner is then provided in the vicinity ofthe latent image, and toner droplets or particles deposit in thevicinity of either the charged or uncharged areas to create a tonedimage on the surface of the photoconductive layer. The resulting tonedimage can be transferred to a suitable ultimate or intermediatereceiving surface, such as paper, or the photoconductive layer canoperate as an ultimate receptor for the image. The imaging process canbe repeated many times to complete a single image, for example, byoverlaying images of distinct color components or effect shadow images,such as overlaying images of distinct colors to form a full color finalimage, and/or to reproduce additional images.

Both single layer and multilayer photoconductive elements have beenused. In single layer embodiments, a charge transport material andcharge generating material are combined with a polymeric binder and thendeposited on the electrically conductive substrate. In multilayerembodiments, the charge transport material and charge generatingmaterial are present in the element in separate layers, each of whichcan optionally be combined with a polymeric binder, deposited on theelectrically conductive substrate. Two arrangements are possible for atwo-layer photoconductive element. In one two-layer arrangement (the“dual layer” arrangement), the charge-generating layer is deposited onthe electrically conductive substrate and the charge transport layer isdeposited on top of the charge generating layer. In an alternatetwo-layer arrangement (the “inverted dual layer” arrangement), the orderof the charge transport layer and charge generating layer is reversed.

In both the single and multilayer photoconductive elements, the purposeof the charge generating material is to generate charge carriers (i.e.,holes and/or electrons) upon exposure to light. The purpose of thecharge transport material is to accept at least one type of these chargecarriers and transport them through the charge transport layer in orderto facilitate discharge of a surface charge on the photoconductiveelement. The charge transport material can be a charge transportcompound, an electron transport compound, or a combination of both. Whena charge transport compound is used, the charge transport compoundaccepts the hole carriers and transports them through the layer with thecharge transport compound. When an electron transport compound is used,the electron transport compound accepts the electron carriers andtransports them through the layer with the electron transport compound.

Organophotoreceptors may be used for both dry and liquidelectrophotography. There are many differences between dry and liquidelectrophotography. In particular, a dry toner is used in dryelectrophotography, whereas a liquid toner is used in liquidelectrophotography. A potential advantage of liquid electrophotographyis that it can provide a higher resolution and thus sharper images thandry electrophotography because liquid toner particles can be muchsmaller than dry toner particles. As a result of their smaller size,liquid toners are able to provide images of higher optical density thandry toners.

In both dry and liquid electrophotography, the charge transport materialused for the organophotoreceptor should be compatible with the polymericbinder in the photoconductive element. The desirability of selecting acompatible polymer binder places a constraint on choosing a suitablepolymeric binder for a particular charge transport material. If thecharge transport material is not compatible with the polymeric binder,the charge transport material may phase-separate or crystallize in thepolymeric binder matrix, or will diffuse onto the surface of the layercontaining the charge transport material. If such incompatibilityoccurs, the organophotoreceptor may cease to transport charges.

Furthermore, liquid electrophotography faces an additional complication.In particular, the organophotoreceptor for liquid electrophotography isin contact with the liquid carrier of a liquid toner as the liquidevaporates and/or is transferred to a receiving surface. As a result,the charge transport material in the photoconductive element may beremoved through extraction by the liquid carrier. Over a long period ofoperation, the amount of the charge transport material removed byextraction may be significant and, therefore, detrimental to theperformance of the organophotoreceptor.

SUMMARY OF THE INVENTION

This invention provides organophotoreceptors having good electrostaticproperties such as high V_(acc) and low V_(dis). This invention alsoprovides charge transport materials having a high compatibility with thepolymeric binder, reduced phase separation, and reduced extraction byliquid carriers.

In a first aspect, an organophotoreceptor comprises an electricallyconductive substrate and a photoconductive element on the electricallyconductive substrate, the photoconductive element comprising:

-   -   (a) a charge transport material having the formula    -   where Y₁ and Y₂ are, each independently, an arylamine group;    -   R₁ and R₂ comprise, each independently, H, an alkyl group, an        alkenyl group, a heterocyclic group, or an aromatic group;    -   X₁ and X₂, each independently, are bridging groups, such as        groups having the formula —(CH₂)_(m)—, branched or linear, where        m is an integer between 0 and 20, inclusive, and one or more of        the methylene groups is optionally replaced by O, S, C═O, O═S═O,        a heterocyclic group, an aromatic group, urethane, urea, an        ester group, an NR₃ group, a CHR₄ group, or a CR₅R₆ group where        R₃, R₄, R₅, and R₆ comprise, each independently, H, hydroxyl        group, thiol group, an alkyl group, an alkenyl group, a        heterocyclic group, or an aromatic group;    -   E₁ and E₂ are, each independently, an epoxy group; and    -   Z is a linking group comprising an alkyl group, an alkenyl        group, a heterocyclic group, or an aromatic group; and    -   (b) a charge generating compound.

The organophotoreceptor may be provided, for example, in the form of aplate, a flexible belt, a flexible disk, a sheet, a rigid drum, or asheet around a rigid or compliant drum. In one embodiment, theorganophotoreceptor includes: (a) a photoconductive element comprisingthe charge transport material, the charge generating compound, a secondcharge transport material, and a polymeric binder; and (b) theelectrically conductive substrate.

In a second aspect, the invention features an electrophotographicimaging apparatus that comprises (a) a light imaging component; and (b)the above-described organophotoreceptor oriented to receive light fromthe light imaging component. The apparatus can further comprise a liquidtoner dispenser. The method of electrophotographic imaging withphotoreceptors containing the above noted charge transport materials isalso described.

In a third aspect, the invention features an electrophotographic imagingprocess that includes (a) applying an electrical charge to a surface ofthe above-described organophotoreceptor; (b) imagewise exposing thesurface of the organophotoreceptor to radiation to dissipate charge inselected areas and thereby form a pattern of at least relatively chargedand uncharged areas on the surface; (c) contacting the surface with atoner, such as a liquid toner that includes a dispersion of colorantparticles in an organic liquid, to create a toned image; and (d)transferring the toned image to a substrate.

In a fourth aspect, the invention features a charge transport materialhaving the general formula above.

In a fifth aspect, the invention features a polymeric charge transportcompound prepared by the reaction of a functional group in a polymericbinder with at least an epoxy group in a compound having the formula

-   -   where Y₁ and Y₂ are, each independently, an arylamine group;    -   R₁ and R₂ comprise, each independently, H, an alkyl group, an        alkenyl group, a heterocyclic group, or an aromatic group;    -   X₁ and X₂, each independently, are bridging groups, such as        groups having the formula —(CH ₂)_(m)—, branched or linear,        where m is an integer between 0 and 20, inclusive, and one or        more of the methylene groups is optionally replaced by O, S,        C═O, O═S═O, a heterocyclic group, an aromatic group, urethane,        urea, an ester group, an NR₃ group, a CHR₄ group, or a CR₅R₆        group where R₃, R₄, R₅, and R₆ comprise, each independently, H,        hydroxyl group, thiol group, an alkyl group, an alkenyl group, a        heterocyclic group, or an aromatic group;    -   E₁ and E₂ are, each independently, an epoxy group; and    -   Z is a linking group comprising an alkyl group, an alkenyl        group, a heterocyclic group, or an aromatic group.

In a sixth aspect, the invention features an organophotoreceptorcomprising an electrically conductive substrate and a photoconductiveelement on the electrically conductive substrate, the photoconductiveelement comprising:

-   -   (a) the polymeric charge transport compound described above; and    -   (b) a charge generating compound.

The invention provides suitable charge transport materials fororganophotoreceptors featuring a combination of good mechanical andelectrostatic properties. These photoreceptors can be used successfullywith liquid toners to produce high quality images. The high quality ofthe imaging system can be maintained after repeated cycling.

Other features and advantages of the invention will be apparent from thefollowing description of the particular embodiments thereof, and fromthe claims.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

An organophotoreceptor, as described herein, has an electricallyconductive substrate and a photoconductive element comprising a chargegenerating compound and a charge transport material having two epoxygroups, each bonded directly or indirectly to an N atom of a hydrazonegroup to form a compound with two linked epoxidated-hydrazone groups.These charge transport materials have desirable properties as evidencedby their performance in organophotoreceptors for electrophotography. Inparticular, the charge transport materials of this invention have highcharge carrier mobilities and good compatibility with various bindermaterials, and possess excellent electrophotographic properties. Theorganophotoreceptors according to this invention generally have a highphotosensitivity, a low residual potential, and a high stability withrespect to cycle testing, crystallization, and organophotoreceptorbending and stretching. The organophotoreceptors are particularly usefulin laser printers and the like as well as fax machines, photocopiers,scanners and other electronic devices based on electrophotography. Theuse of these charge transport materials is described in more detailbelow in the context of laser printer use, although their application inother devices operating by electrophotography can be generalized fromthe discussion below.

To produce high quality images, particularly after multiple cycles, itis desirable for the charge transport materials to form a homogeneoussolution with the polymeric binder and remain approximatelyhomogeneously distributed through the organophotoreceptor materialduring the cycling of the material. In addition, it is desirable toincrease the amount of charge that the charge transport material canaccept (indicated by a parameter known as the acceptance voltage or“V_(acc)”), and to reduce retention of that charge upon discharge(indicated by a parameter known as the discharge voltage or “V_(dis)”).

The charge transport materials can be classified as a charge transportcompound or an electron transport compound. There are many chargetransport compounds and electron transport compounds known in the artfor electrophotography. Non-limiting examples of charge transportcompounds include, for example, pyrazoline derivatives, fluorenederivatives, oxadiazole derivatives, stilbene derivatives, enaminederivatives, enamine stilbene derivatives, hydrazone derivatives,carbazole hydrazone derivatives, (N,N-disubstituted)arylamines such astriaryl amines, polyvinyl carbazole, polyvinyl pyrene,polyacenaphthylene, or multi-hydrazone compounds comprising at least twohydrazone groups and at least two groups selected from the groupconsisting of (N,N-disubstituted)arylamine such as triphenylamine andheterocycles such as carbazole, julolidine, phenothiazine, phenazine,phenoxazine, phenoxathiin, thiazole, oxazole, isoxazole,dibenzo(1,4)dioxin, thianthrene, imidazole, benzothiazole,benzotriazole, benzoxazole, benzimidazole, quinoline, isoquinoline,quinoxaline, indole, indazole, pyrrole, purine, pyridine, pyridazine,pyrimidine, pyrazine, triazole, oxadiazole, tetrazole, thiadiazole,benzisoxazole, benzisothiazole, dibenzofuran, dibenzothiophene,thiophene, thianaphthene, quinazoline, or cinnoline.

Non-limiting examples of electron transport compounds include, forexample, bromoaniline, tetracyanoethylene, tetracyanoquinodimethane,2,4,7-trinitro-9-fluorenone, 2,4,5,7-tetranitro-9-fluorenone,2,4,5,7-tetranitroxanthone, 2,4,8-trinitrothioxanthone,2,6,8-trinitro-indeno[1,2-b]thiophene-4-one, and 1,3,7-trinitrodibenzothiophene-5,5-dioxide, (2,3-diphenyl-1-indenylidene)malononitrile,4H-thiopyran-1,1-dioxide and its derivatives such as4-dicyanomethylene-2,6-diphenyl-4H-thiopyran-1,1-dioxide,4-dicyanomethylene-2,6-di-m-tolyl-4H-thiopyran-1,1-dioxide, andunsymmetrically substituted 2,6-diaryl-4H-thiopyran-1,1-dioxide such as4H-1,1-dioxo-2-(p-isopropylphenyl)-6-phenyl-4-(dicyanomethylidene)thiopyranand4H-1,1-dioxo-2-(p-isopropylphenyl)-6-(2-thienyl)-4-(dicyanomethylidene)thiopyran,derivatives of phospha-2,5-cyclohexadiene,alkoxycarbonyl-9-fluorenylidene)malononitrile derivatives such as(4-n-butoxycarbonyl-9-fluorenylidene)malononitrile,(4-phenethoxycarbonyl-9-fluorenylidene)malononitrile,(4-carbitoxy-9-fluorenylidene)malononitrile, anddiethyl(4-n-butoxycarbonyl-2,7-dinitro-9-fluorenylidene)-malonate,anthraquinodimethane derivatives such as11,11,12,12-tetracyano-2-alkylanthraquinodimethane and11,11-dicyano-12,12-bis(ethoxycarbonyl)anthraquinodimethane, anthronederivatives such as 1-chloro-10-[bis(ethoxycarbonyl)methylene]anthrone,1,8-dichloro-110-[bis(ethoxy carbonyl) methylene]anthrone,1,8-dihydroxy-110-[bis(ethoxycarbonyl)methylene] anthrone, and1-cyano-10-[bis(ethoxycarbonyl)methylene)anthrone,7-nitro-2-aza-9-fluroenylidene-malononitrile, diphenoquinonederivatives, benzoquinone derivatives, naphtoquinone derivatives,quinine derivatives, tetracyanoethylenecyanoethylene, 2,4,8-trinitrothioxantone, dinitrobenzene derivatives, dinitroanthracene derivatives,dinitroacridine derivatives, nitroanthraquinone derivatives,dinitroanthraquinone derivatives, succinic anhydride, maleic anhydride,dibromo maleic anhydride, pyrene derivatives, carbazole derivatives,hydrazone derivatives, N,N-dialkylaniline derivatives, diphenylaminederivatives, triphenylamine derivatives, triphenylmethane derivatives,tetracyano quinoedimethane, 2,4,5,7-tetranitro-9-fluorenone,2,4,7-trinitro-9-dicyanomethylene fluorenone, 2,4,5,7-tetranitroxanthonederivatives, and 2,4,8-trinitrothioxanthone derivatives. In someembodiments of interest, the electron transport compound comprises an(alkoxycarbonyl-9-fluorenylidene)malononitrile derivative, such as(4-n-butoxycarbonyl-9-fluorenylidene)malononitrile.

Although there are many charge transport materials available, there is aneed for other charge transport materials to meet the variousrequirements of particular electrophotography applications.

In electrophotography applications, a charge-generating compound withinan organophotoreceptor absorbs light to form electron-hole pairs. Theseelectrons and holes can be transported over an appropriate time frameunder a large electric field to discharge locally a surface charge thatis generating the field. The discharge of the field at a particularlocation results in a surface charge pattern that essentially matchesthe pattern drawn with the light. This charge pattern then can be usedto guide toner deposition. The charge transport materials describedherein are especially effective at transporting charge, and inparticular holes from the electron-hole pairs formed by the chargegenerating compound. In some embodiments, a specific electron transportcompound or charge transport compound can also be used along with thecharge transport material of this invention.

The layer or layers of materials containing the charge generatingcompound and the charge transport materials are within anorganophotoreceptor. To print a two dimensional image using theorganophotoreceptor, the organophotoreceptor has a two dimensionalsurface for forming at least a portion of the image. The imaging processthen continues by cycling the organophotoreceptor to complete theformation of the entire image and/or for the processing of subsequentimages.

The organophotoreceptor may be provided in the form of a plate, aflexible belt, a disk, a rigid drum, a sheet around a rigid or compliantdrum, or the like. The charge transport material can be in the samelayer as the charge generating compound and/or in a different layer fromthe charge generating compound. Additional layers can be used also, asdescribed further below.

In some embodiments, the organophotoreceptor material comprises, forexample:

-   -   (a) a charge transport layer comprising the charge transport        material and a polymeric binder; (b) a charge generating layer        comprising the charge generating compound and a polymeric        binder; and (c) the electrically conductive substrate. The        charge transport layer may be intermediate between the charge        generating layer and the electrically conductive substrate.        Alternatively, the charge generating layer may be intermediate        between the charge transport layer and the electrically        conductive substrate. In further embodiments, the        organophotoreceptor material has a single layer with both a        charge transport material and a charge generating compound        within a polymeric binder.

The organophotoreceptors can be incorporated into an electrophotographicimaging apparatus, such as laser printers. In these devices, an image isformed from physical embodiments and converted to a light image that isscanned onto the organophotoreceptor to form a surface latent image. Thesurface latent image can be used to attract toner onto the surface ofthe organophotoreceptor, in which the toner image is the same or thenegative of the light image projected onto the organophotoreceptor. Thetoner can be a liquid toner or a dry toner. The toner is subsequentlytransferred, from the surface of the organophotoreceptor, to a receivingsurface, such as a sheet of paper. After the transfer of the toner, theentire surface is discharged, and the material is ready to cycle again.The imaging apparatus can further comprise, for example, a plurality ofsupport rollers for transporting a paper receiving medium and/or formovement of the photoreceptor, a light imaging component with suitableoptics to form the light image, a light source, such as a laser, a tonersource and delivery system and an appropriate control system.

An electrophotographic imaging process generally can comprise (a)applying an electrical charge to a surface of the above-describedorganophotoreceptor; (b) imagewise exposing the surface of theorganophotoreceptor to radiation to dissipate charge in selected areasand thereby form a pattern of charged and uncharged areas on thesurface; (c) exposing the surface with a toner, such as a liquid tonerthat includes a dispersion of colorant particles in an organic liquid tocreate a toner image, to attract toner to the charged or dischargedregions of the organophotoreceptor; and (d) transferring the toner imageto a substrate.

As described herein, an organophotoreceptor comprises a charge transportmaterial having the formula

-   -   where Y₁ and Y₂ are, each independently, an arylamine group;    -   R₁ and R₂ comprise, each independently, H, an alkyl group, an        alkenyl group, a heterocyclic group, or an aromatic group;    -   X₁ and X₂, each independently, are bridging groups, such as        groups having the formula —(CH₂)_(m)—, branched or linear, where        m is an integer between 0 and 20, inclusive, and one or more of        the methylene groups is optionally replaced by O, S, C═O, O═S═O,        a heterocyclic group, an aromatic group, urethane, urea, an        ester group, an NR₃ group, a CHR₄ group, or a CR₅R₆ group where        R₃, R₄, R₅, and R₆ comprise, each independently, H, hydroxyl        group, thiol group, an alkyl group, an alkenyl group, a        heterocyclic group, or an aromatic group;    -   E₁ and E₂ are, each independently, an epoxy group; and    -   Z is a linking group comprising an alkyl group, an alkenyl        group, a heterocyclic group, or an aromatic group.

The aromatic group can be any conjugated system containing 4n+2π-electrons. There are many criteria available for determiningaromaticity. A widely employed criterion for the quantitative assessmentof aromaticity is the resonance energy. In general, the resonance energyof the aromatic group is greater than 10 KJ/mol. Aromatic groups may beclassified as an aromatic heterocyclic group which contains at least aheteroatom in the 4n+2 π-electron ring, or as an aryl group which doesnot contain a heteroatom in the 4n+2 π-electron ring. Nonetheless,either the aromatic heterocyclic or the aryl group may have at least oneheteroatom in a substituent attached to the 4n+2 π-electron ring.Furthermore, either the aromatic heterocyclic or the aryl group maycomprise a monocyclic or polycyclic (such as bicyclic, tricyclic, etc.)aromatic ring.

Non-limiting examples of the aromatic heterocyclic group are furanyl,thiophenyl, pyrrolyl, indolyl, carbazolyl, benzofuranyl,benzothiophenyl, dibenzofuranyl, dibenzothiophenyl, pyridinyl,pyridazinyl, pyrimidinyl, pyrazinyl, triazinyl, tetrazinyl, petazinyl,quinolinyl, isoquinolinyl, cinnolinyl, phthalazinyl, quinazolinyl,quinoxalinyl, naphthyridinyl, pteridinyl, acridinyl, phenanthridinyl,phenanthrolinyl, anthyridinyl, purinyl, pteridinyl, alloxazinyl,phenazinyl, phenothiazinyl, phenoxazinyl, phenoxathiinyl,dibenzo(1,4)dioxinyl, thianthrenyl, and a combination thereof. Thearomatic heterocyclic group may also include any combination of theabove aromatic heterocyclic groups bonded together either by a bond (asin bicarbazolyl) or by a linking group (as in1,6-di(10H-10-phenothiazinyl)hexane). The linking group may include analiphatic group, an aromatic group, a heterocyclic group, or acombination thereof. Furthermore, either an aliphatic group or anaromatic group within a linking group may comprise at least oneheteroatom such as O, S, and N.

Non-limiting examples of the aryl group are phenyl, naphthyl, benzyl, ortolanyl group, sexiphenylene, phenanthrenyl, anthracenyl, coronenyl, andtolanylphenyl. The aryl group may also include any combination of theabove aryl groups bonded together either by a bond (as in biphenylgroup) or by a linking group (as in stilbenyl, diphenyl sulfone, anarylamine group). The linking group may include an aliphatic group, anaromatic group, a heterocyclic group, or a combination thereof.Furthermore, either an aliphatic group or an aromatic group within alinking group may comprise at least one heteroatom such as O, S, and N.

An arylamine group includes an (N,N-disubstituted)arylamine group (e.g.,triarylamine group, alkyldiarylamine group, and dialkylarylamine group),julolidinyl group, and a carbazolyl group.

Substitution is liberally allowed on the chemical groups to affectvarious physical effects on the properties of the compounds, such asmobility, sensitivity, solubility, compatibility, stability, and thelike, as is known generally in the art. In the description of chemicalsubstituents, there are certain practices common to the art that arereflected in the use of language. The term group indicates that thegenerically recited chemical entity (e.g., alkyl group, alkenyl group,aromatic group, epoxy group, arylamine group, etc.) may have anysubstituent thereon which is consistent with the bond structure of thatgroup. For example, where the term ‘alkyl group’ is used, that termwould not only include unsubstituted linear, branched and cyclic alkyls,such as methyl, ethyl, isopropyl, tert-butyl, cyclohexyl, dodecyl andthe like, but also substituents having heteroatom such as3-ethoxylpropyl, 4-(N-ethylamino)butyl, 3-hydroxypentyl, 2-thio]hexyl,1,2,3-tribromoopropyl, and the like. However, as is consistent with suchnomenclature, no substitution would be included within the term thatwould alter the fundamental bond structure of the underlying group. Forexample, where a phenyl group is recited, substitution such as1-aminophenyl, 2,4-dihydroxyphenyl, 1,3,5-trithiophenyl,1,3,5-trimethoxyphenyl and the like would be acceptable within theterminology, while substitution of 1,1,2,2,3,3-hexamethylphenyl wouldnot be acceptable as that substitution would require the ring bondstructure of the phenyl group to be altered to a non-aromatic formbecause of the substitution. When referring to an epoxy group, thesubstituent cited will include any substitution that does not destroythe 3-membered ring structure of the epoxy group. Where the term moietyis used, such as alkyl moiety or phenyl moiety, that terminologyindicates that the chemical moiety is not substituted. When referring toan alkyl moiety, the term represents only an unsubstituted alkylhydrocarbon group, whether branched, straight chain, or cyclic.

Organophotoreceptors

The organophotoreceptor may be, for example, in the form of a plate, asheet, a flexible belt, a disk, a rigid drum, or a sheet around a rigidor compliant drum, with flexible belts and rigid drums generally beingused in commercial embodiments. The organophotoreceptor may comprise,for example, an electrically conductive substrate and on theelectrically conductive substrate a photoconductive element in the formof one or more layers. The photoconductive element can comprise both acharge transport material and a charge generating compound in apolymeric binder, which may or may not be in the same layer, as well asa second charge transport material such as a charge transport compoundor an electron transport compound in some embodiments. For example, thecharge transport material and the charge generating compound can be in asingle layer. In other embodiments, however, the photoconductive elementcomprises a bilayer construction featuring a charge generating layer anda separate charge transport layer. The charge generating layer may belocated intermediate between the electrically conductive substrate andthe charge transport layer. Alternatively, the photoconductive elementmay have a structure in which the charge transport layer is intermediatebetween the electrically conductive substrate and the charge generatinglayer.

The electrically conductive substrate may be flexible, for example inthe form of a flexible web or a belt, or inflexible, for example in theform of a drum. A drum can have a hollow cylindrical structure thatprovides for attachment of the drum to a drive that rotates the drumduring the imaging process. Typically, a flexible electricallyconductive substrate comprises an electrically insulating substrate anda thin layer of electrically conductive material onto which thephotoconductive material is applied.

The electrically insulating substrate may be paper or a film formingpolymer such as polyester (e.g., polyethylene terephthalate orpolyethylene naphthalate), polyimide, polysulfone, polypropylene, nylon,polyester, polycarbonate, polyvinyl resin, polyvinyl fluoride,polystyrene and the like. Specific examples of polymers for supportingsubstrates included, for example, polyethersulfone (Stabar™ S-100,available from ICI), polyvinyl fluoride (Tedlar®, available from E.I.DuPont de Nemours & Company), polybisphenol-A polycarbonate (Makrofol™,available from Mobay Chemical Company) and amorphous polyethyleneterephthalate (Melinar™, available from ICI Americas, Inc.). Theelectrically conductive materials may be graphite, dispersed carbonblack, iodine, conductive polymers such as polypyrroles and Calgon®conductive polymer 261 (commercially available from Calgon® Corporation,Inc., Pittsburgh, Pa.), metals such as aluminum, titanium, chromium,brass, gold, copper, palladium, nickel, or stainless steel, or metaloxide such as tin oxide or indium oxide. In embodiments of particularinterest, the electrically conductive material is aluminum. Generally,the photoconductor substrate has a thickness adequate to provide therequired mechanical stability. For example, flexible web substratesgenerally have a thickness from about 0.01 to about 1 mm, while drumsubstrates generally have a thickness from about 0.5 mm to about 2 mm.

The charge generating compound is a material that is capable ofabsorbing light to generate charge carriers, such as a dye or pigment.Non-limiting examples of suitable charge generating compounds include,for example, metal-free phthalocyanines (e.g., ELA 8034 metal-freephthalocyanine available from H.W. Sands, Inc. or Sanyo Color Works,Ltd., CGM-X₀₁), metal phthalocyanines such as titanium phthalocyanine,copper phthalocyanine, oxytitanium phthalocyanine (also referred to astitanyl oxyphthalocyanine, and including any crystalline phase ormixtures of crystalline phases that can act as a charge generatingcompound), hydroxygallium phthalocyanine, squarylium dyes and pigments,hydroxy-substituted squarylium pigments, perylimides, polynuclearquinones available from Allied Chemical Corporation under the trade nameIndofast® Double Scarlet, Indofast® Violet Lake B, Indofast® BrilliantScarlet and Indofast® Orange, quinacridones available from DuPont underthe trade name Monastral™ Red, Monastral™ Violet and Monastral™ Red Y,naphthalene 1,4,5,8-tetracarboxylic acid derived pigments including theperinones, tetrabenzoporphyrins and tetranaphthaloporphyrins, indigo-and thioindigo dyes, benzothioxanthene-derivatives, perylene3,4,9,10-tetracarboxylic acid derived pigments, polyazo-pigmentsincluding bisazo-, trisazo- and tetrakisazo-pigments, polymethine dyes,dyes containing quinazoline groups, tertiary amines, amorphous selenium,selenium alloys such as selenium-tellurium, selenium-tellurium-arsenicand selenium-arsenic, cadmium sulphoselenide, cadmium selenide, cadmiumsulphide, and mixtures thereof. For some embodiments, the chargegenerating compound comprises oxytitanium phthalocyanine (e.g., anyphase thereof), hydroxygallium phthalocyanine or a combination thereof.

The photoconductive layer of this invention may optionally contain asecond charge transport material which may be a charge transportcompound, an electron transport compound, or a combination of both.Generally, any charge transport compound or electron transport compoundknown in the art can be used as the second charge transport material.

An electron transport compound and a UV light stabilizer can have asynergistic relationship for providing desired electron flow within thephotoconductor. The presence of the UV light stabilizers alters theelectron transport properties of the electron transport compounds toimprove the electron transporting properties of the composite. UV lightstabilizers can be ultraviolet light absorbers or ultraviolet lightinhibitors that trap free radicals.

UV light absorbers can absorb ultraviolet radiation and dissipate it asheat. UV light inhibitors are thought to trap free radicals generated bythe ultraviolet light and after trapping of the free radicals,subsequently to regenerate active stabilizer moieties with energydissipation. In view of the synergistic relationship of the UVstabilizers with electron transport compounds, the particular advantagesof the UV stabilizers may not be their UV stabilizing abilities,although the UV stabilizing ability may be further advantageous inreducing degradation of the organophotoreceptor over time. The improvedsynergistic performance of organophotoreceptors with layers comprisingboth an electron transport compound and a UV stabilizer are describedfurther in copending U.S. patent application Ser. No. 10/425,333 filedon Apr. 28, 2003 to Zhu, entitled “Organophotoreceptor With A LightStabilizer,” incorporated herein by reference.

Non-limiting examples of suitable light stabilizer include, for example,hindered trialkylamines such as Tinuvin 144 and Tinuvin 292 (from CibaSpecialty Chemicals, Terrytown, N.Y.), hindered alkoxydialkylamines suchas Tinuvin 123 (from Ciba Specialty Chemicals), benzotriazoles such asTinuvan 328, Tinuvin 900 and Tinuvin 928 (from Ciba SpecialtyChemicals), benzophenones such as Sanduvor 3041 (from Clariant Corp.,Charlotte, N.C.), nickel compounds such as Arbestab (from RobinsonBrothers Ltd, West Midlands, Great Britain), salicylates,cyanocinnamates, benzylidene malonates, benzoates, oxanilides such asSanduvor VSU (from Clariant Corp., Charlotte, N.C.), triazines such asCyagard UV-1164 (from Cytec Industries Inc., N.J.), polymeric stericallyhindered amines such as Luchem (from Atochem North America, Buffalo,N.Y.). In some embodiments, the light stabilizer is selected from thegroup consisting of hindered trialkylamines having the followingformula:

where R₁, R₂, R₃, R₄, R₆, R₇, R₈, R₁₀, R₁₁, R₁₂, R₁₃, R₁₄, R₁₅ are, eachindependently, hydrogen, alkyl group, or ester, or ether group; and R₅,R₉, and R₁₄ are, each independently, alkyl group; and X is a linkinggroup selected from the group consisting of —O—CO—(CH₂)_(m)—CO—O— wherem is between 2 to 20.

Optionally, the photoconductive layer may comprise a crosslinking agentlinking the charge transport compound and the binder. As is generallytrue for crosslinking agents in various contexts, the crosslinking agentcomprises a plurality of functional groups or at least one functionalgroup with the ability to exhibit multiple functionality. Specifically,a suitable crosslinking agent generally comprises at least onefunctional group that reacts with an epoxy group and at least onefunctional group that reacts with a functional group of the polymericbinder. Non-limiting examples of suitable functional groups for reactingwith the epoxy group include hydroxyl, thiol, an amino group, carboxylgroup, or a combination thereof. In some embodiments, the functionalgroup of the crosslinking agent for reacting with the polymeric binderdoes not react significantly with the epoxy group. In general, a personof ordinary skill in the art can select the appropriate functional groupof the crosslinking agent to react with the polymeric binder, orsimilarly, a person of ordinary skill in the art can select appropriatefunctional groups of the polymeric binder to react with the functionalgroup of the crosslinking agent. Suitable functional groups of thecrosslinking agent that do not react significantly with the epoxy group,at least under selected conditions, include, for example, epoxy groups,aldehydes and ketones. Suitable reactive binder functional groups forreacting with the aldehydes and ketones include, for example, amines.

In some embodiments, the crosslinking agent is a cyclic acid anhydride,which effectively is at least bifunctional. Non-limiting examples ofsuitable cyclic acid anhydrides include, for example, 1,8-naphthalenedicarboxylic acid anhydride, itaconic anhydride, glutaric anhydride andcitraconic anhydride, fumaric anhydride, phthalic anhydride, isophthalicanhydride, and terephthalic anhydride with maleic anhydride and phthalicanhydride being of particular interest.

The binder generally is capable of dispersing or dissolving the chargetransport compound (in the case of the charge transport layer or asingle layer construction) and/or the charge generating compound (in thecase of the charge generating layer or a single layer construction).Examples of suitable binders for both the charge generating layer andcharge transport layer generally include, for example,polystyrene-co-butadiene, polystyrene-co-acrylonitrile, modified acrylicpolymers, polyvinyl acetate, styrene-alkyd resins, soya-alkyl resins,polyvinylchloride, polyvinylidene chloride, polyacrylonitrile,polycarbonates, polyacrylic acid, polyacrylates, polymethacrylates,styrene polymers, polyvinyl butyral, alkyd resins, polyamides,polyurethanes, polyesters, polysulfones, polyethers, polyketones,phenoxy resins, epoxy resins, silicone resins, polysiloxanes,poly(hydroxyether) resins, polyhydroxystyrene resins, novolak,poly(phenylglycidyl ether)-co-dicyclopentadiene, copolymers of monomersused in the above-mentioned polymers, and combinations thereof. In someembodiments, the binder comprises a polymer with a reactive hydrogenfunctionality, such as hydroxyl, thiol, an amino group, carboxyl group,or a combination thereof, that can react with the epoxy ring of thecharge transport compounds of this invention or with a functional groupof a crosslinking agent, such as a cyclic acid anhydride. In theorganophotoreceptor, the functional group of the polymer can be bondeddirectly with the epoxy group or indirectly through a co-reactivecrosslinking agent, for example, a cyclic acid anhydride group, to formthe corresponding and predictable reaction product. Suitable binderswith reactive functionality include, for example, polyvinyl butyral,such as BX-1 and BX-5 form Sekisui Chemical Co. Ltd., Japan.

Suitable optional additives for any one or more of the layers include,for example, antioxidants, coupling agents, dispersing agents, curingagents, surfactants, and combinations thereof.

The photoconductive element overall typically has a thickness from about10 microns to about 45 microns. In the dual layer embodiments having aseparate charge generating layer and a separate charge transport layer,charge generation layer generally has a thickness form about 0.5 micronsto about 2 microns, and the charge transport layer has a thickness fromabout 5 microns to about 35 microns. In embodiments in which the chargetransport material and the charge generating compound are in the samelayer, the layer with the charge generating compound and the chargetransport composition generally has a thickness from about 7 microns toabout 30 microns. In embodiments with a distinct electron transportlayer, the electron transport layer has an average thickness from about0.5 microns to about 10 microns and in further embodiments from about 1micron to about 3 microns. In general, an electron transport overcoatlayer can increase mechanical abrasion resistance, increases resistanceto carrier liquid and atmospheric moisture, and decreases degradation ofthe photoreceptor by corona gases. A person of ordinary skill in the artwill recognize that additional ranges of thickness within the explicitranges above are contemplated and are within the present disclosure.

Generally, for the organophotoreceptors described herein, the chargegeneration compound is in an amount from about 0.5 to about 25 weightpercent, in further embodiments in an amount from about 1 to about 15weight percent, and in other embodiments in an amount from about 2 toabout 10 weight percent, based on the weight of the photoconductivelayer. The charge transport material is in an amount from about 10 toabout 80 weight percent, based on the weight of the photoconductivelayer, in further embodiments in an amount from about 35 to about 60weight percent, and in other embodiments from about 45 to about 55weight percent, based on the weight of the photoconductive layer. Theoptional second charge transport material, when present, can be in anamount of at least about 2 weight percent, in other embodiments fromabout 2.5 to about 25 weight percent, based on the weight of thephotoconductive layer, and in further embodiments in an amount fromabout 4 to about 20 weight percent, based on the weight of thephotoconductive layer. The binder is in an amount from about 15 to about80 weight percent, based on the weight of the photoconductive layer, andin further embodiments in an amount from about 20 to about 75 weightpercent, based on the weight of the photoconductive layer. A person ofordinary skill in the art will recognize that additional ranges withinthe explicit ranges of compositions are contemplated and are within thepresent disclosure.

For the dual layer embodiments with a separate charge generating layerand a charge transport layer, the charge generation layer generallycomprises a binder in an amount from about 10 to about 90 weightpercent, in further embodiments from about 15 to about 80 weight percentand in some embodiments in an amount from about 20 to about 75 weightpercent, based on the weight of the charge generation layer. Theoptional charge transport material in the charge generating layer, ifpresent, generally can be in an amount of at least about 2.5 weightpercent, in further embodiments from about 4 to about 30 weight percentand in other embodiments in an amount from about 10 to about 25 weightpercent, based on the weight of the charge generating layer. The chargetransport layer generally comprises a binder in an amount from about 20weight percent to about 70 weight percent and in further embodiments inan amount from about 30 weight percent to about 50 weight percent. Aperson of ordinary skill in the art will recognize that additionalranges of binder concentrations for the dual layer embodiments withinthe explicit ranges above are contemplated and are within the presentdisclosure.

For the embodiments with a single layer having a charge generatingcompound and a charge transport material, the photoconductive layergenerally comprises a binder, a charge transport material, and a chargegeneration compound. The charge generation compound can be in an amountfrom about 0.05 to about 25 weight percent and in further embodiment inan amount from about 2 to about 15 weight percent, based on the weightof the photoconductive layer. The charge transport material can be in anamount from about 10 to about 80 weight percent, in other embodimentsfrom about 25 to about 65 weight percent, in additional embodiments fromabout 30 to about 60 weight percent and in further embodiments in anamount from about 35 to about 55 weight percent, based on the weight ofthe photoconductive layer, with the remainder of the photoconductivelayer comprising the binder, and optional additives, such as anyconventional additives. A single layer with a charge transportcomposition and a charge generating compound generally comprises abinder in an amount from about 10 weight percent to about 75 weightpercent, in other embodiments from about 20 weight percent to about 60weight percent, and in further embodiments from about 25 weight percentto about 50 weight percent. Optionally, the layer with the chargegenerating compound and the charge transport material may comprise asecond charge transport material. The optional second charge transportmaterial, if present, generally can be in an amount of at least about2.5 weight percent, in further embodiments from about 4 to about 30weight percent and in other embodiments in an amount from about 10 toabout 25 weight percent, based on the weight of the photoconductivelayer. A person of ordinary skill in the art will recognize thatadditional composition ranges within the explicit compositions rangesfor the layers above are contemplated and are within the presentdisclosure.

In general, any layer with an electron transport compound canadvantageously further include a UV light stabilizer. In particular, theelectron transport layer generally can comprise an electron transportcompound, a binder, and an optional UV light stabilizer. An overcoatlayer comprising an electron transport compound is described further incopending U.S. patent application Ser. No. 10/396,536 to Zhu et al.entitled, “Organophotoreceptor With An Electron Transport Layer,”incorporated herein by reference. For example, an electron transportcompound as described above may be used in the release layer of thephotoconductors described herein. The electron transport compound in anelectron transport layer can be in an amount from about 10 to about 50weight percent, and in other embodiments in an amount from about 20 toabout 40 weight percent, based on the weight of the electron transportlayer. A person of ordinary skill in the art will recognize thatadditional ranges of compositions within the explicit ranges arecontemplated and are within the present disclosure.

The UV light stabilizer, if present, in any one or more appropriatelayers of the photoconductor generally is in an amount from about 0.5 toabout 25 weight percent and in some embodiments in an amount from about1 to about 10 weight percent, based on the weight of the particularlayer. A person of ordinary skill in the art will recognize thatadditional ranges of compositions within the explicit ranges arecontemplated and are within the present disclosure.

For example, the photoconductive layer may be formed by dispersing ordissolving the components, such as one or more of a charge generatingcompound, the charge transport material of this invention, a secondcharge transport material such as a charge transport compound or anelectron transport compound, a UV light stabilizer, and a polymericbinder in organic solvent, coating the dispersion and/or solution on therespective underlying layer and drying the coating. In particular, thecomponents can be dispersed by high shear homogenization, ball-milling,attritor milling, high energy bead (sand) milling or other sizereduction processes or mixing means known in the art for effectingparticle size reduction in forming a dispersion.

The photoreceptor may optionally have one or more additional layers aswell. An additional layer can be, for example, a sub-layer or anovercoat layer, such as a barrier layer, a release layer, a protectivelayer, or an adhesive layer. A release layer or a protective layer mayform the uppermost layer of the photoconductor element. A barrier layermay be sandwiched between the release layer and the photoconductiveelement or used to overcoat the photoconductive element. The barrierlayer provides protection from abrasion to the underlayers. An adhesivelayer locates and improves the adhesion between a photoconductiveelement, a barrier layer and a release layer, or any combinationthereof. A sub-layer is a charge blocking layer and locates between theelectrically conductive substrate and the photoconductive element. Thesub-layer may also improve the adhesion between the electricallyconductive substrate and the photoconductive element.

Suitable barrier layers include, for example, coatings such ascrosslinkable siloxanol-colloidal silica coating and hydroxylatedsilsesquioxane-colloidal silica coating, and organic binders such aspolyvinyl alcohol, methyl vinyl ether/maleic anhydride copolymer,casein, polyvinyl pyrrolidone, polyacrylic acid, gelatin, starch,polyurethanes, polyimides, polyesters, polyamides, polyvinyl acetate,polyvinyl chloride, polyvinylidene chloride, polycarbonates, polyvinylbutyral, polyvinyl acetoacetal, polyvinyl formal, polyacrylonitrile,polymethyl methacrylate, polyacrylates, polyvinyl carbazoles, copolymersof monomers used in the above-mentioned polymers, vinyl chloride/vinylacetate/vinyl alcohol terpolymers, vinyl chloride/vinyl acetate/maleicacid terpolymers, ethylene/vinyl acetate copolymers, vinylchloride/vinylidene chloride copolymers, cellulose polymers, andmixtures thereof. The above barrier layer polymers optionally maycontain small inorganic particles such as fumed silica, silica, titania,alumina, zirconia, or a combination thereof. Barrier layers aredescribed further in U.S. Pat. No. 6,001,522 to Woo et al., entitled“Barrier Layer For Photoconductor Elements Comprising An Organic PolymerAnd Silica,” incorporated herein by reference. The release layer topcoatmay comprise any release layer composition known in the art. In someembodiments, the release layer is a fluorinated polymer, siloxanepolymer, fluorosilicone polymer, silane, polyethylene, polypropylene,polyacrylate, or a combination thereof. The release layers can comprisecrosslinked polymers.

The release layer may comprise, for example, any release layercomposition known in the art. In some embodiments, the release layercomprises a fluorinated polymer, siloxane polymer, fluorosiliconepolymer, polysilane, polyethylene, polypropylene, polyacrylate,poly(methyl methacrylate-co-methacrylic acid), urethane resins,urethane-epoxy resins, acrylated-urethane resins, urethane-acrylicresins, or a combination thereof. In further embodiments, the releaselayers comprise crosslinked polymers.

The protective layer can protect the organophotoreceptor from chemicaland mechanical degradation. The protective layer may comprise anyprotective layer composition known in the art. In some embodiments, theprotective layer is a fluorinated polymer, siloxane polymer,fluorosilicone polymer, polysilane, polyethylene, polypropylene,polyacrylate, poly(methyl methacrylate-co-methacrylic acid), urethaneresins, urethane-epoxy resins, acrylated-urethane resins,urethane-acrylic resins, or a combination thereof. In some embodimentsof particular interest, the release layers are crosslinked polymers.

An overcoat layer may comprise an electron transport compound asdescribed further in copending U.S. patent application Ser. No.10/396,536, filed on Mar. 25, 2003 to Zhu et al. entitled,“Organoreceptor With An Electron Transport Layer,” incorporated hereinby reference. For example, an electron transport compound, as describedabove, may be used in the release layer of this invention. The electrontransport compound in the overcoat layer can be in an amount from about2 to about 50 weight percent, and in other embodiments in an amount fromabout 10 to about 40 weight percent, based on the weight of the releaselayer. A person of ordinary skill in the art will recognize thatadditional ranges of composition within the explicit ranges arecontemplated and are within the present disclosure.

Generally, adhesive layers comprise a film forming polymer, such aspolyester, polyvinylbutyral, polyvinylpyrrolidone, polyurethane,polymethyl methacrylate, poly(hydroxy amino ether) and the like. Barrierand adhesive layers are described further in U.S. Pat. No. 6,180,305 toAckley et al., entitled “Organic Photoreceptors for LiquidElectrophotography,” incorporated herein by reference.

Sub-layers can comprise, for example, polyvinylbutyral, organosilanes,hydrolyzable silanes, epoxy resins, polyesters, polyamides,polyurethanes, and the like. In some embodiments, the sub-layer has adry thickness between about 20 Angstroms and about 2,000 Angstroms.Sublayers containing metal oxide conductive particles can be betweenabout 1 and about 25 microns thick. A person of ordinary skill in theart will recognize that additional ranges of compositions and thicknesswithin the explicit ranges are contemplated and are within the presentdisclosure.

The charge transport materials as described herein, and photoreceptorsincluding these compounds, are suitable for use in an imaging processwith either dry or liquid toner development. For example, any dry tonersand liquid toners known in the art may be used in the process and theapparatus of this invention. Liquid toner development can be desirablebecause it offers the advantages of providing higher resolution imagesand requiring lower energy for image fixing compared to dry toners.Examples of suitable liquid toners are known in the art. Liquid tonersgenerally comprise toner particles dispersed in a carrier liquid. Thetoner particles can comprise a colorant/pigment, a resin binder, and/ora charge director. In some embodiments of liquid toner, a resin topigment ratio can be from 1:1 to 10:1, and in other embodiments, from4:1 to 8:1. Liquid toners are described further in Published U.S. PatentApplications 2002/0128349, entitled “Liquid Inks Comprising A StableOrganosol,” 2002/0086916, entitled “Liquid Inks Comprising TreatedColorant Particles,” and 2002/0197552, entitled “Phase Change DeveloperFor Liquid Electrophotography,” all three of which are incorporatedherein by reference.

Charge Transport Material

As described herein, an organophotoreceptor comprises a charge transportmaterial having the formula

-   -   where Y₁ and Y₂ are, each independently, an arylamine group;    -   R₁ and R₂ comprise, each independently, H, an alkyl group, an        alkenyl group, a heterocyclic group, or an aromatic group;    -   X₁ and X₂, each independently, are bridging groups, such as        groups having the formula —(CH₂)_(m)—, branched or linear, where        m is an integer between 0 and 20, inclusive, and one or more of        the methylene groups is optionally replaced by O, S, C═O, O═S═O,        a heterocyclic group, an aromatic group, urethane, urea, an        ester group, an NR₃ group, a CHR₄ group, or a CR₅R₆ group where        R₃, R₄, R₅, and R₆ comprise, each independently, H, hydroxyl        group, thiol group, an alkyl group, an alkenyl group, a        heterocyclic group, or an aromatic group;    -   E₁ and E₂ are, each independently, an epoxy group; and    -   Z is a linking group comprising an alkyl group, an alkenyl        group, a heterocyclic group, or an aromatic group.

Specific, non-limiting examples of suitable charge transport materialswithin the general Formula (1) of the present invention have thefollowing structures:

Synthesis Of Charge Transport Materials

The synthesis of the charge transport materials of this invention can beprepared by the following multi-step synthetic procedure, although othersuitable procedures can be used by a person of ordinary skill in the artbased on the disclosure herein.

The first step is a nucleophilic substitution reaction between a linkingorganic compound having two halogen groups (i.e. dibromoalkanes or4,4′-dichlorodiphenyl sulfone) and hydrazine hydrate. The linkingorganic compound may or may not be symmetric with respect to the twohalogen groups. The reaction mixture may be refluxed for 24 hours. Theproduct of the nucleophilic substitution is the corresponding aromaticcompound having two hydrazine groups, such as 4,4′-dihydrazinodiphenylsulfone. In the second step, the aromatic compound having two hydrazinegroups may react with an arylamine having an aldehyde or a keto group toform the corresponding aromatic compound having two hydrazone groups. Ifdesired, two different arylamine compounds can be reacted with thedi-hydrazine compound. The use of one or two arylamine reactants withketo groups result in a charge transport material with R₁ and/or R₂groups that differ from H. While the use of two different arylaminecompounds may result in a mixture of products, a person of ordinaryskill in the art can reduce the synthesis of undesired forms of productthrough either sequential or simultaneous reactions, and the differentproduct compounds can be separated from each other through appropriatepurification approaches.

In the third step, the two NH groups of the aromatic compound having twohydrazone groups may react with an organic halide comprising an epoxygroup in the presence of an alkaline to form a charge transport materialhaving two epoxidated-hydrazone groups bonded together through a linkinggroup. Non-limiting examples of suitable organic halide comprising anepoxy group for this invention are epihalohydrins, such asepichlorohydrin. The organic halide comprising an epoxy group may alsobe prepared by the epoxidation reaction of the corresponding organichalide having an olefin group. The epoxidation reaction is described inCarey et al., “Advanced Organic Chemistry, Part B: Reactions andSynthesis,” New York, 1983, pp. 494-498, incorporated herein byreference. The organic halide having an olefin group may be prepared bythe Wittig reaction between a suitable organic halide having an aldehydeor keto group and a suitable Wittig reagent. The Wittig and relatedreactions are described in Carey et al., “Advanced Organic Chemistry,Part B: Reactions and Synthesis,” New York, 1983, pp. 69-77,incorporated herein by reference.

Depending on the particular reactivities of the groups, the order ofsome of the reactions may be changed.

As noted above, the epoxy groups can be reacted with functional groupsof a polymer binder directly or through a crosslinking agent. Thereactions of epoxy groups with appropriate functional groups aredescribed further in C. A. May, editor, “Epoxy Resins Chemistry AndTechnology,” (Marcel Dekker, New York, 1988) and in B. Ellis, editor,“Chemistry And Technology Of Epoxy Resins,” (Blackie Academic AndProfessional, London, 1993), both of which are incorporated herein byreference.

In general, the charge transport material is combined with the binderand any other components of the particular layer of theorganophotoreceptor for forming the particular layer. If a crosslinkingagent is used, it may be desirable to react the crosslinking agent firstwith either the charge transport material or with the polymer binderbefore combining the other ingredients. A person of ordinary skill inthe art can evaluate the appropriate reaction order, such as combiningall of the components at one time or sequentially, for forming the layerwith desired properties.

The invention will now be described further by way of the followingexamples.

EXAMPLES Example 1 Synthesis And Characterization Charge TransportMaterials

This example described the synthesis and characterization of Compound(2) in which the numbers refer to formula numbers above. Thecharacterization involves the chemical characterization, and theelectronic characterization of materials formed with the compound isdescribed in the subsequent examples.

Compound (2)

A suspension of 4,4′-dichlorodiphenyl sulfone (20 g, 0.069 mol, obtainedfrom Aldrich) in hydrazine hydrate (158 ml, obtained from Aldrich) wasrefluxed for 24 hours. The mixture was cooled to room temperature andcrystals precipitated out. The crystals were filtered off and washed 3times with water and one time with isopropanol. The yield of theproduct, 4,4′-dihydrazinodiphenyl sulfone, was 15.75 g (81.8%). Theproduct had a melting point of 193-194° C. The literature procedure forthe preparation of 4,4′-dihydrazinodiphenyl sulfone was published inKhimiya Geterotsiklicheskikh Soedinenii, 11, p. 1508-1510, 1980 (issuedin the Republic of Latvia). The article is incorporated herein byreference.

A mixture of 4-(diphenylamino)benzaldehyde (25 g, 0.09 mol, obtainedfrom Aldrich), 4,4′-dihydrazinodiphenyl sulfone (11.37 g, 0.041 mol) and80 ml of dioxane was added to a 250 ml round bottom flask equipped witha reflux condenser and a magnetic stirrer. The reaction mixture washeated at 50° C. for 2 hours with stirring. The solvent was removed byevaporation to form 4,4′-dihydrazondiphenyl sulfonetriphenylaminohydrazone. The yield was 30.1 g (93.4%).

A mixture of 4,4′-dihydrazondiphenyl sulfone triphenylaminohydrazone(30.1 g, 0.038 mol) and epichlorohydrin (68 ml, 0.855 mol, obtained fromAldrich) was added to a 250 ml 3-neck round bottom flask equipped with areflux condenser, a thermometer and a magnetic stirrer. The reactionmixture was stirred vigorously at 35-40° C. for 7 hours. During thistime, powdered 85% potassium hydroxide (KOH, 11.3 g, 0.171 mol) andanhydrous sodium sulfate (Na₂SO₄, 9 g, 0.0228 mol) were added in threeportions with prior cooling of the reaction mixture to 20-25° C. Afterthe termination of the reaction, the mixture was cooled to roomtemperature and filtered. The organic part was treated with ethylacetate and washed with distilled water until the washed water becameneutral. The organic layer was dried over anhydrous magnesium sulfate,treated with activated charcoal, and filtered. The solvents wereevaporated to form Compound (2). Compound (2) was purified by columnchromatography (silica gel, grade 62, 60-200 mesh, 150 Å, Aldrich) usinga mixture of acetone and hexane in a ratio of 1:4 by volume as theeluant. The fractions containing Compound (2) were collected, and thesolvents were evaporated. Compound (2) was recrystallized from a mixtureof acetone and hexane in a ratio of 1:4 by volume and dried at 50° C. ina vacuum oven for 6 hours. The yield of Compound (2) was 19.3 g (56%).Compound (2) had a melting point of 223-225° C. The ¹H NMR spectrum (100MHz) of Compound (2) in CDCl₃ was characterized by the followingchemical shifts (δ, ppm): 8.0-6.8 (m, 38H, CH═N, Ar); 4.5-4.3 (dd, 2H,one proton of NCH₂); 4.1-3.8 (dd, 2H, another proton of NCH₂); 3.2 (m,2H, CH); 2.9-2.8 (dd, 2H, one proton of OCH₂); 2.7-2.5 (dd, anotherproton of OCH₂). An elemental analysis yielded the following results inweight percent: C 74.71; H 5.33; N 9.45, which compared with calculatedvalues for C₃₈H₃₅N₅O₂, in weight percent of: C 74.64; H 5.37; N 9.33.

Compound (3)

Compound (3) may be prepared according to the procedure for Compound (2)except that 4-(diphenylamino)benzaldehyde is replaced with9-ethyl-3-carbazole carboxaldehyde (commercially available from Aldrich,Milwaukee, Wis.).

Compound (4)

Compound (4) may be prepared according to the procedure for Compound (2)except that 4-(diphenylamino)benzaldehyde is replaced with julolidinealdehyde, which may be prepared according to the following procedure.Julolidine (100 g, 0.6 moles, obtained from Aldrich Chemicals Co,Milwaukee, Wis.) was dissolved in DMF (200 ml, obtained from Aldrich) ina 500 ml three neck round bottom flask. The flask was cooled to 0° C. inan ice bath. Phosphorus oxychloride (POCl₃, 107 g, 0.7 mole, Aldrich)was added dropwise while the temperature was kept below 5° C. After theaddition of POCl₃ was completed, the flask was placed in a steam bathand stirred for a period of 1 hour. The flask was cooled to roomtemperature, and the solution was added slowly to a large excess ofdistilled water with a vigorous stirring. The stirring was continued for2 hours. The solid that formed was filtered off and washed repeatedlywith water until the washed water became neutral. The product,julolidine aldehyde, was dried in a vacuum oven at 50° C. for 4 hours.

Example 2 Charge Mobility Measurements

This example describes the measurement of charge mobility for chargetransport materials, such as Compound (2) described above.

Sample 1

A mixture of 0.1 g of Compound (2) and 0.1 g of polycarbonate Z-200(from Mitsubishi Gas Chemical) was dissolved in 2 ml of tetrahydrofuran.The solution was coated on a polyester film with conductive aluminumlayer with a dip roller. After the coating was dried for 1 hour at 80°C., a clear 10 μm thick layer was formed. The hole mobility of thesample was measured. The results are presented in Table 1.

Mobility Measurements

Each sample was corona charged positively up to a surface potential Uand illuminated with 2 ns long nitrogen laser light pulse. The holemobility p was determined as described in Kalade et al., “Investigationof charge carrier transfer in electrophotographic layers of chalkogenideglasses,” Proceeding IPCS 1994: The Physics and Chemistry of ImagingSystems, Rochester, N.Y., pp. 747-752, incorporated herein by reference.The hole mobility measurement was repeated with changes to the chargingregime to charge the sample to different U values, which corresponded todifferent electric field strength, E, inside the layer. This dependenceon electric field strength was approximated by the formulaμ=μ₀ e ^(α{square root}{square root over (E)})

Here E is electric field strength, μ₀ to is the zero field mobility andα is Pool-Frenkel parameter. Table 1 lists the mobility characterizingparameters μ₀ and α values and the mobility value at the 6.4×10⁵ V/cmfield strength as determined from these measurements. TABLE 1 μ (cm²/V ·s) at Ionization μ₀ 6.4 · 10⁵ Potential Sample (cm²/V4 · s) V/cm α(cm/V)^(0.5) (eV) 1 5 · 10⁻⁹ 1.1 · 10⁻⁶ 0.0068 5.47 [Compound (2)]

Example 3 Ionization Potential Measurements

This example describes the measurement of the ionization potential forthe charge transport materials, such as Compound (2) described inExample 1.

To perform the ionization potential measurements, a thin layer of chargetransport material about 0.5 μm thickness was coated from a solution of2 mg of charge transport material in 0.2 ml of tetrahydrofuran on a 20cm² substrate surface. The substrate was polyester film with an aluminumlayer over a methylcellulose sublayer of about 0.4 μm thickness.

Ionization potential was measured as described in Grigalevicius et al.,“3,6-Di(N-diphenylamino)-9-phenylcarbazole and its methyl-substitutedderivative as novel hole-transporting amorphous molecular materials,”Synthetic Metals 128 (2002), p. 127-131, incorporated herein byreference. In particular, each sample was illuminated with monochromaticlight from the quartz monochromator with a deuterium lamp source. Thepower of the incident light beam was 2−5·10⁻⁸ W. A negative voltage of−300 V was supplied to the sample substrate. A counter-electrode withthe 4.5×15 mm² slit for illumination was placed at 8 mm distance fromthe sample surface. The counter-electrode was connected to the input ofa BK2-16 type electrometer, working in the open input regime, for thephotocurrent measurement. A 10⁻¹⁵−10⁻¹² amp photocurrent was flowing inthe circuit under illumination. The photocurrent, I, was stronglydependent on the incident light photon energy hν. The I^(0.5)=f(hν)dependence was plotted. Usually, the dependence of the square root ofphotocurrent on incident light quanta energy is well described by linearrelationship near the threshold (see references “Ionization Potential ofOrganic Pigment Film by Atmospheric Photoelectron Emission Analysis,”Electrophotography, 28, Nr. 4, p. 364 (1989) by E. Miyamoto, Y.Yamaguchi, and M. Yokoyama; and “Photoemission in Solids,” Topics inApplied Physics, 26, 1-103 (1978) by M. Cordona and L. Ley, both ofwhich are incorporated herein by reference). The linear part of thisdependence was extrapolated to the hv axis, and the Ip value wasdetermined as the photon energy at the interception point. Theionization potential measurement has an error of ±0.03 eV. Table 1 liststhe ionization potential value of Compound (2).

As understood by those skilled in the art, additional substitution,variation among substituents, and alternative methods of synthesis anduse may be practiced within the scope and intent of the presentdisclosure of the invention. The embodiments above are intended to beillustrative and not limiting. Additional embodiments are within theclaims. Although the present invention has been described with referenceto particular embodiments, workers skilled in the art will recognizethat changes may be made in form and detail without departing from thespirit and scope of the invention.

1. An organophotoreceptor comprising an electrically conductivesubstrate and a photoconductive element on the electrically conductivesubstrate, the photoconductive element comprising: (a) a chargetransport material having the formula

where Y₁ and Y₂ are, each independently, an arylamine group; R₁ and R₂comprise, each independently, H, an alkyl group, an alkenyl group, aheterocyclic group, or an aromatic group; X₁ and X₂, each independently,are bridging groups; E₁ and E₂ are, each independently, an epoxy group;and Z is a linking group comprising an alkyl group, an alkenyl group, aheterocyclic group, or an aromatic group; and (b) a charge generatingcompound.
 2. An organophotoreceptor according to claim 1 wherein Zcomprises an aromatic group.
 3. An organophotoreceptor according toclaim 1 wherein Y₁ and Y₂ are, each independently, a carbazolyl group,an (N,N-disubstituted)arylamine group, or a julolidinyl group.
 4. Anorganophotoreceptor according to claim 1 wherein E₁ and E₂ are, eachindependently, an oxiranyl ring.
 5. An organophotoreceptor according toclaim 1 wherein the charge transport material is selected from the groupof compounds represented by the following formula:

where Y₁ and Y₂ are, each independently, an arylamine group.
 6. Anorganophotoreceptor according to claim 1 wherein X₁ and X₂, eachindependently, have the formula —(CH ₂)_(m)—, branched or linear, wherem is an integer between 0 and 20, inclusive, and one or more of themethylene groups is optionally replaced by O, S, C═O, O═S═O, aheterocyclic group, an aromatic group, urethane, urea, an ester group,an NR₃ group, a CHR₄ group, or a CR₅R₆ group where R₃, R₄, R₅, and R₆comprise, each independently, H, hydroxyl group, thiol group, an alkylgroup, an alkenyl group, a heterocyclic group, or an aromatic group. 7.An organophotoreceptor according to claim 1 wherein the photoconductiveelement further comprises a second charge transport material.
 8. Anorganophotoreceptor according to claim 7 wherein the second chargetransport material comprises an electron transport compound.
 9. Anorganophotoreceptor according to claim 1 wherein the photoconductiveelement further comprises a binder.
 10. An electrophotographic imagingapparatus comprising: (a) a light imaging component; and (b) anorganophotoreceptor oriented to receive light from the light imagingcomponent, the organophotoreceptor comprising an electrically conductivesubstrate and a photoconductive element on the electrically conductivesubstrate, the photoconductive element comprising: (i) a chargetransport material having the formula

where Y₁ and Y₂ are, each independently, an arylamine group; R₁ and R₂comprise, each independently, H, an alkyl group, an alkenyl group, aheterocyclic group, or an aromatic group; X₁ and X₂, each independently,are bridging groups; E₁ and E₂ are, each independently, an epoxy group;and Z is a linking group comprising an alkyl group, an alkenyl group, aheterocyclic group, or an aromatic group; and (ii) a charge generatingcompound.
 11. An electrophotographic imaging apparatus according toclaim 10 wherein Z comprises an aromatic group.
 12. Anelectrophotographic imaging apparatus according to claim 10 wherein Y₁and Y₂ are, each independently, a carbazolyl group, an(N,N-disubstituted)arylamine group, or a julolidinyl group.
 13. Anelectrophotographic imaging apparatus according to claim 10 wherein E₁and E₂ are, each independently, an oxiranyl ring.
 14. Anelectrophotographic imaging apparatus according to claim 10 wherein thecharge transport material is selected from the group of compoundsrepresented by the following formula:

where Y₁ and Y₂ are, each independently, an arylamine group.
 15. Anelectrophotographic imaging apparatus according to claim 10 wherein X₁and X₂, each independently, have the formula —(CH ₂)_(m)—, branched orlinear, where m is an integer between 0 and 20, inclusive, and one ormore of the methylene groups is optionally replaced by O, S, C═O, O═S═O,a heterocyclic group, an aromatic group, urethane, urea, an ester group,an NR₃ group, a CHR₄ group, or a CR₅R₆ group where R₃, R₄, R₅, and R₆comprise, each independently, H, hydroxyl group, thiol group, an alkylgroup, an alkenyl group, a heterocyclic group, or an aromatic group. 16.An electrophotographic imaging apparatus according to claim 10 whereinthe photoconductive element further comprises a second charge transportmaterial.
 17. An electrophotographic imaging apparatus according toclaim 16 wherein second charge transport material comprises an electrontransport compound.
 18. An electrophotographic imaging apparatusaccording to claim 10 further comprising a liquid toner dispenser. 19.An electrophotographic imaging process comprising; (a) applying anelectrical charge to a surface of an organophotoreceptor comprising anelectrically conductive substrate and a photoconductive element on theelectrically conductive substrate, the photoconductive elementcomprising (i) a charge transport material having the formula

where Y₁ and Y₂ are, each independently, an arylamine group; R₁ and R₂comprise, each independently, H, an alkyl group, an alkenyl group, aheterocyclic group, or an aromatic group; X₁ and X₂, each independently,are bridging groups; E₁ and E₂ are, each independently, an epoxy group;and Z is a linking group comprising an alkyl group, an alkenyl group, aheterocyclic group, or an aromatic group; and (ii) a charge generatingcompound. (b) imagewise exposing the surface of the organophotoreceptorto radiation to dissipate charge in selected areas and thereby form apattern of charged and uncharged areas on the surface; (c) contactingthe surface with a toner to create a toned image; and (d) transferringthe toned image to substrate.
 20. An electrophotographic imaging processaccording to claim 19 wherein Z comprises an aromatic group.
 21. Anelectrophotographic imaging process according to claim 19 wherein Y₁ andY₂ are, each independently, a carbazolyl group, an(N,N-disubstituted)arylamine group, or a julolidinyl group.
 22. Anelectrophotographic imaging process according to claim 19 wherein E₁ andE₂ are, each independently, an oxiranyl ring.
 23. An electrophotographicimaging process according to claim 19 wherein the charge transportmaterial is selected from the group of compounds represented by thefollowing formula:

where Y₁ and Y₂ are, each independently, an arylamine group.
 24. Anelectrophotographic imaging process according to claim 19 wherein X₁ andX₂, each independently, have the formula —(CH₂)_(m)—, branched orlinear, where m is an integer between 0 and 20, inclusive, and one ormore of the methylene groups is optionally replaced by O, S, C═O, O═S═O,a heterocyclic group, an aromatic group, urethane, urea, an ester group,an NR₃ group, a CHR₄ group, or a CR₅R₆ group where R₃, R₄, R₅, and R₆comprise, each independently, H, hydroxyl group, thiol group, an alkylgroup, an alkenyl group, a heterocyclic group, or an aromatic group 25.An electrophotographic imaging process according to claim 19 wherein thephotoconductive element further comprises a second charge transportmaterial.
 26. An electrophotographic imaging process according to claim25 wherein the second charge transport material comprises an electrontransport compound.
 27. An electrophotographic imaging process accordingto claim 19 wherein the photoconductive element further comprises abinder.
 28. An electrophotographic imaging process according to claim 19wherein the toner comprises a liquid toner comprising a dispersion ofcolorant particles in an organic liquid.
 29. A charge transport materialhaving the formula

where Y₁ and Y₂ are, each independently, an arylamine group; R₁ and R₂comprise, each independently, H, an alkyl group, an alkenyl group, aheterocyclic group, or an aromatic group; X₁ and X₂, each independently,are bridging groups; E₁ and E₂ are, each independently, an epoxy group;and Z is a linking group comprising an alkyl group, an alkenyl group, aheterocyclic group, or an aromatic group.
 30. A charge transportmaterial according to claim 29 wherein Z comprises an aromatic group.31. A charge transport material according to claim 29 wherein Y₁ and Y₂are, each independently, a carbazolyl group, an(N,N-disubstituted)arylamine group, or a julolidinyl group.
 32. A chargetransport material according to claim 29 wherein E₁ and E₂ are, eachindependently, an oxiranyl ring.
 33. A charge transport materialaccording to claim 29 wherein the charge transport material is selectedfrom the group of compounds represented by the following formula:

where Y₁ and Y₂ are, each independently, an arylamine group.
 34. Acharge transport material according to claim 29 wherein X₁ and X₂, eachindependently, have the formula —(CH ₂)_(m)—, branched or linear, wherem is an integer between 0 and 20, inclusive, and one or more of themethylene groups is optionally replaced by O, S, C═O, O═S═O, aheterocyclic group, an aromatic group, urethane, urea, an ester group,an NR₃ group, a CHR₄ group, or a CR₅R₆ group where R₃, R₄, R₅, and R₆comprise, each independently, H, hydroxyl group, thiol group, an alkylgroup, an alkenyl group, a heterocyclic group, or an aromatic group 35.A polymeric charge transport material prepared by the reaction of afunctional group in a polymeric binder with at least an epoxy group of acompound having the formula

where Y₁ and Y₂ are, each independently, an arylamine group; R₁ and R₂comprise, each independently, H, an alkyl group, an alkenyl group, aheterocyclic group, or an aromatic group; X₁ and X₂, each independently,are bridging groups; E₁ and E₂ are, each independently, an epoxy group;and Z is a linking group comprising an alkyl group, an alkenyl group, aheterocyclic group, or an aromatic group.
 36. A polymeric chargetransport material according to claim 35 wherein the functional group ofthe binder is selected from the group consisting of hydroxyl group,carboxyl group, an amino group, and thiol group.
 37. A polymeric chargetransport material according to claim 35 wherein a crosslinking agent isbonded between the epoxy group and the functional group of the binder.38. A polymeric charge transport material according to claim 35 whereinZ comprises an aromatic group.
 39. A polymeric charge transport materialaccording to claim 35 wherein Y₁ and Y₂ are, each independently, acarbazolyl group, an (N,N-disubstituted)arylamine group, or ajulolidinyl group.
 40. A polymeric charge transport material accordingto claim 35 wherein X₁ and X₂, each independently, have the formula —(CH₂)_(m)—, branched or linear, where m is an integer between 0 and 20,inclusive, and one or more of the methylene groups is optionallyreplaced by O, S, C═O, O═S═O, a heterocyclic group, an aromatic group,urethane, urea, an ester group, an NR₃ group, a CHR₄ group, or a CR₅R₆group where R₃, R₄, R₅, and R₆ comprise, each independently, H, hydroxylgroup, thiol group, an alkyl group, an alkenyl group, a heterocyclicgroup, or an aromatic group
 41. An organophotoreceptor comprising anelectrically conductive substrate and a photoconductive element on theelectrically conductive substrate, the photoconductive elementcomprising: (a) a polymeric charge transport material prepared by thereaction of a functional group in a polymeric binder with at least anepoxy group of a compound having the formula

where Y₁ and Y₂ are, each independently, an arylamine group; R₁ and R₂comprise, each independently, H, an alkyl group, an alkenyl group, aheterocyclic group, or an aromatic group; X₁ and X₂, each independently,are bridging groups; E₁ and E₂ are, each independently, an epoxy group;and Z is a linking group comprising an alkyl group, an alkenyl group, aheterocyclic group, or an aromatic group; and (b) a charge generatingcompound.
 42. An organophotoreceptor according to claim 41 wherein thephotoconductive element further comprises a second charge transportmaterial.
 43. An organophotoreceptor according to claim 42 wherein thesecond charge transport material comprises an electron transportcompound.
 44. An organophotoreceptor according to claim 41 wherein thefunctional group of the binder is selected from the group consisting ofhydroxyl group, carboxyl group, an amino group, and thiol group.
 45. Anorganophotoreceptor according to claim 41 wherein Z comprises anaromatic group.
 46. An organophotoreceptor according to claim 41 whereinY₁ and Y₂ are, each independently, a carbazolyl group, an(N,N-disubstituted)arylamine group, or a julolidinyl group.
 47. Anorganophotoreceptor according to claim 2 wherein the aromatic groupcomprises two aryl groups bonded together by a linking group.
 48. Anorganophotoreceptor according to claim 47 wherein the two aryl groupsare phenylene and the linking group comprises S, O, N, or SO₂.
 49. Anelectrophotographic imaging apparatus according to claim 11 wherein thearomatic group comprises two aryl groups bonded together by a linkinggroup.
 50. An electrophotographic imaging apparatus according to claim49 wherein the two aryl groups are phenylene and the linking groupcomprises S, O, N, or SO₂.
 51. An electrophotographic imaging processaccording to claim 20 wherein the aromatic group comprises two arylgroups bonded together by a linking group.
 52. An electrophotographicimaging process according to claim 51 wherein the two aryl groups arephenylene and the linking group comprises S, O, N, or SO₂.
 53. A chargetransport material according to claim 29 wherein the aromatic groupcomprises two aryl groups bonded together by a linking group.
 54. Acharge transport material according to claim 53 wherein the two arylgroups are phenylene and the linking group comprises S, O, N, or SO₂.55. A polymeric charge transport material according to claim 38 whereinthe aromatic group comprises two aryl groups bonded together by alinking group.
 56. A polymeric charge transport material according toclaim 55 wherein the two aryl groups are phenylene and the linking groupcomprises S, O, N, or SO₂.
 57. An organophotoreceptor according to claim45 wherein the aromatic group comprises two aryl groups bonded togetherby a linking group.
 58. An organophotoreceptor according to claim 57wherein the two aryl groups are phenylene and the linking groupcomprises S, O, N, or SO₂.